Alternative erythropoietin-mediated signaling prevents secondary microvascular thrombosis and inflammation within cutaneous burns

Subcutaneous Anti-inflammatory Therapies to Prevent Burn Progression in a Swine Model of Contact Burn Injury

INTRODUCTION

If left untreated, burn injuries can deepen or progress in depth within the first 72 hours after injury as a result of increased wound inflammation, subsequently worsening healing outcomes. This can be especially detrimental to warfighters who are constrained to resource-limited environments with delayed evacuation times to higher roles of care and more effective treatment. Preventing this burn progression at the point of injury has the potential to improve healing outcomes but requires a field-deployable therapy and delivery system. Subcutaneous therapies known to treat inflammation delivered local to the wound site may prove to be one such avenue for success.

MATERIALS AND METHODS

Seven Yorkshire-cross swine received partial-thickness burn injuries using a previously established contact burn model. Each animal received one of the seven therapies: (1) saline, (2) heparin, (3) ibuprofen, (4) erythropoietin, (5) resolvin, (6) rapamycin, and (7) placental extract, all of which are either currently employed or are experimental in field use and indicated to treat inflammation. Treatments were delivered subcutaneously on the day of injury and 24 hours post-injury to simulate a prolonged field care scenario, before potential evacuation. Animals and wound development were observed for 28 days before euthanasia. Throughout the course of the study, wounds were observed macroscopically via non-invasive imaging. Histological analyses provided the critical metric of burn progression. Treatment success criteria were designated as the ability to prevent burn progression past 80% of the dermal depth in two of the three treated wounds, a clinically relevant metric of burn progression.

RESULTS

It was determined that the applied model successfully created reproducible partial-thickness burn injuries in this porcine study. No significant differences with regard to lateral wound size or the rate of lateral wound closure were observed in any treatments. Several treatments including resolvin, rapamycin, ibuprofen, and erythropoietin successfully reduced burn progression to less than 80% of the dermal depth in two of the three wounds, 24 hours after injury.

CONCLUSIONS

This report employs an established model of porcine contact burn injury in order to test the ability of local subcutaneous delivery of therapeutics to prevent burn progression at the point of injury, via what is believed to be the inhibition of inflammation. Several treatments successfully prevented burn progression to a full-thickness injury, potentially improving wound healing outcomes in a simulated battlefield scenario. Subcutaneously administered therapies combating burn-induced inflammation at the point of injury may serve as a field-deployable treatment modality to improve warfighter recovery and return to duty.

Characteristics of blood clotting on thromboelastography in patients with early burns

BACKGROUND

Thromboelastography (TEG) is a viscoelastic test that may be used to evaluate the hemostatic function of whole blood, and it may be useful for burn patients with multiple hemostatic defects.

METHODS

We retrospectively recruited patients with burns between January 2019 and July 2021. Blood samples were drawn on admission and subjected to coagulation parameter assessment, including conventional coagulation tests and TEG assessment. Receiver operating characteristic (ROC) analysis was performed to predict the occurrence of complications in patients with early burns.

RESULTS

Ninety-three patients with early burns met the inclusion criteria. Patients with minor, moderate, severe, and extremely severe burns accounted for 19.4 %, 36.6 %, 16.1 %, and 27.9 % of all patients, respectively. Compared with the healthy controls, patients with early burns showed significant reductions in the R and K values, and significant elevation in the maximum amplitude (MA), coagulation index (CI), and alpha angle. Compared with minor and moderate burn patients, patients with severe and extremely severe burns had lower K values and thrombin time and higher alpha angle, CI, prothrombin time, international normalized ratio, D-dimer, and fibrin degradation products. Patients with hypercoagulation had lower R and K values, longer MA, longer CI, and greater alpha angle. After ROC analysis, the areas under the ROC curve for acute lung injury, acute kidney injury, and bleeding were 0.789, 0.802, and 0.900, respectively.

CONCLUSION

TEG provides insight into the hemostatic state of patients with early burns, and can predict complications in early burn patients when combined with conventional coagulation tests.

Early cutaneous inflammatory response at different degree of burn and its significance for clinical diagnosis and management

A complete characterization of the burn wound based on cutaneous architectural changes and inflammatory response is extremely important to provide evidence for progressive changes in the burn wound. Burn wounds are highly susceptible to conversion into deeper wounds, which need special care and attention; thereby, the complete characterization of burn wound type and their subsequent inflammatory status in the cutaneous system at the earliest is of paramount importance. Inflammatory markers at different degrees will help clinicians devise better and more specific treatment strategies for each burn type. The present study is carried out to profile pro-inflammatory gene expression along with immune cell quantification, vascular perfusion, and histopathological assessment in the cutaneous system of murine models. The study revealed that burn injury caused an immediate increase in vascular perfusion in superficial and partial-thickness burns, whereas there was a decrease in vascular perfusion in full-thickness burns. An influx of lymphocytes at the edges of burn wounds in each type of burn injury was well-orchestrated with the event of vascular perfusion. Further, pro-inflammatory gene expression profiling revealed significant upregulation vis-à-vis upregulation of TNF-α and MCP-1 genes, with an increase in the number of neutrophils following 72 h of injury that evidently cemented the conversion of superficial burn into partial-thickness burn. The molecular findings were profoundly supported by the histopathological changes. Thus, our foundational studies show distinct characteristic cutaneous changes correlated with the expression of key pro-inflammatory genes in three different types of burn injuries. Characterization of these cutaneous inflammatory responses provides a promising future for medical interventions involved with different degrees of burn injury, and it will also help in the pre-clinical testing of therapies for burn injury.

Evaluation of Platelet Distribution Width as an Early Predictor of Acute Kidney Injury in Extensive Burn Patients

Background

The extensive burns devastate trauma. The research was designed to analyse the predictive value of early platelet (PLT) indices on the development of acute kidney injury (AKI) after severe burns.

Methods and Results

186 patients with extensive burns (burn area ≥30%) were eventually involved. Multivariate analyses pointed out that platelet distribution width (PDW) in the first 24 h after admission was an independent risk factor for AKI, severe AKI, and RRT requirement in patients with severe burns, and AKI risk showed an increase of 30.9% per increase of 1% in PDW (OR = 1.309, CI, 1.075-1.594, and P = 0.007). It was found that the area under the ROC curve (AUC) of PDW predicting AKI was 0.735 and that the AUC value was 0.81 for AKI after combining PDW and blood urea nitrogen (BUN). Based on the cut-off value PDW = 17.7%, patients were divided into high- (PDW ≥17.7%) and low-risk (PDW <17.7%) groups. In the KM analysis, there was a higher cumulative incidence of AKI if patients were in a high-risk group (in 30 days); and the stages of AKI showed a linear upward trend (chi-square test for linear trend P  <  0.001) as there was an increase in the risk level.

Conclusion

The PDW level in the early stage serves as an important risk factor for AKI, severe AKI, and RRT requirement in extensive burns. When PDW >17.7%, burn patients are not only at a higher risk for AKI but may also have higher AKI severity. Due to low cost and wide availability, PDW has the potential to be the tool that can predict AKI in extensive burn patients.

Burn wound conversion: clinical implications for the treatment of severe burns

The identification of novel treatments for severe burn wounds relies on accurate clinical assessments of the extent of injury. However, evaluation of burn wound depth can be challenging due to the tendency for burn wounds to progress over time in a little-understood process known as 'burn wound conversion'. Local factors affecting the burn wound, such as inflammation, oxidative stress-induced tissue damage, vasostasis and bacterial infections, lead to increased cell death by apoptosis or oncosis, while systemic events may promote burn wound conversion. Acute shock, metabolic derangements, age or immunomodulation can modify cytokine secretion, lower immune responses, decrease blood flow or cause bacterial infection at the burn wound site. Therefore, therapeutic approaches targeting specific mechanisms that reduce cell death, improve wound reperfusion and promote tissue regrowth should favourably enhance burn wound healing, and long-term functional and aesthetic outcomes. Our current understanding of these mechanisms mostly comes from animal studies, underscoring the need for extensive research in humans. A streamlined approach would be to investigate the parallels in other disease states that exhibit ischaemia and potential reperfusion, such as ischaemic stroke and myocardial infarction. Moreover, in view of the limited knowledge available on the subject, the need exists for further clinical research into burn wound conversion and novel target pathways to ameliorate its effects. This review describes events that affect the viability of cells at the burn wound site resulting in burn wound conversion, and identifies potential targets for clinical interventions that may diminish burn wound conversion.

Current understanding of the chronic stress response to burn injury from human studies

There is a marked inflammatory and hypermetabolic response following a burn injury. The interlinked responses are more pronounced than for other forms of trauma and can persist for ≥3 years post-injury in burned patients. After a burn, patients have an increased risk of diseases of ageing including cancer, diabetes and cardiovascular disease, highlighting the need for effective long-term strategies to ameliorate the stress response post-burn. Current therapeutic strategies for post-burn recovery include removal of damaged tissue with surgical excision and wound repair, nutritional supplementation and rehabilitative exercise. These strategies aim to minimize the hypermetabolic and inflammatory responses, as well as reducing the loss of lean body mass. This review briefly summarises the inflammatory and hypermetabolic responses and provides an update on the current therapeutic strategies for burned patients. The review examines the persistent nutritional challenge of ensuring sufficient energy intake of each macronutrient to fuel the hypermetabolic and counteract the catabolic response of burn injury, whilst reducing periods of hyperglycaemia and hypertriglyceridemia. Patients require individualized treatment options tailored to unique systemic responses following a burn, facilitated by a precision medicine approach to improve clinical and physiological outcomes in burned patients. Thus, this review discusses the utility of metabolic flexibility assessment to aid clinical decision making and prescription relating to nutritional supplementation and rehabilitative exercise in the burned patient.

Research advances in prevention and treatment of burn wound deepening in early stage

The burn wound is a dynamic living environment that is affected by many factors. It may present a progressive expansion of necrosis into the initially viable zone of stasis within a short time postburn. Therefore, how to salvage of the zone of stasis is of crucial importance in prevention and treatment strategies of burn wound progressive deepening. This review focuses on the cellular basis of tissue injury and the current progress of prevention and treatment strategies of burn wound progressive deepening, in order to provide references for the treatment of burn wounds in the early phase.

Nonerythropoietic Erythropoietin Mimetic Peptide ARA290 Ameliorates Chronic Stress-Induced Depression-Like Behavior and Inflammation in Mice

Major depressive disorder (MDD) is a highly prevalent psychiatric disorder. But the treatment of depression remains challenging. Anti-inflammatory treatments frequently produce antidepressant effects. EPO-derived helix-B peptide ARA290 has been reported to retain the anti-inflammatory and tissue-protective functions of EPO without erythropoiesis-stimulating effects. The effects of ARA290 on MDD remain elusive. This study established chronic unpredictable mild stress and chronic social defeat stress mouse models. Daily administration of ARA290 during chronic stress induction in two mouse models ameliorated depression-like behavior, similar to fluoxetine. With marginal effects on peripheral blood hemoglobin and red cells, ARA290 and fluoxetine reversed chronic stress-induced increased frequencies and/or numbers of CD11b+Ly6Ghi neutrophils and CD11b+Ly6Chi monocytes in the bone marrow and meninges. Furthermore, both drugs reversed chronic stress-induced microglia activation. Thus, ARA290 ameliorated chronic stress-induced depression-like behavior in mice through, at least partially, its anti-inflammatory effects.

A modified burn comb model with a new dorsal frame that allows for local treatment in partial-thickness burns in rats

Burn wound progression (BWP) leads to vertical and horizontal injury extension. The "burn comb model" is commonly used, in which a full-thickness burn with intercalated unburned interspaces is induced. We aimed to establish an injury progressing to the intermediate dermis, allowing repeated wound evaluation. Furthermore, we present a new dorsal frame that enables topical drug application. 8 burn field and 6 interspaces were induced on each of 17 rats' dorsa with a 10-second burn comb application. A developed 8-panel aluminum frame was sutured onto 12 animals and combined with an Elizabethan collar. Over 14 days, macroscopic & histologic wound assessment and Laser-Speckle-Contrast-Imaging (LSCI) were performed besides evaluation of frame durability. The 10-second group was compared to 9 animals injured with a full-thickness 60-second model. Frame durability was sufficient up to day 4 with 8 of 12 frames (67%) still mounted. The 60-second burn led to an increased extent of interspace necrosis (p=0.002). The extent of necrosis increased between days 1 and 2 (p=0.001), following the 10-second burn (24%±SEM 8% to 40%±SEM 6%) and the 60-second burn (57%±SEM 6% to 76%±SEM 4%). Interspace LSCI perfusion was higher than burn field perfusion. It earlier reached baseline levels in the 10-second group (on day 1: 142%±SEM 9% vs. 60%±SEM 5%; p<0.001). Within day 1, the 10-second burn showed histological progression to the intermediate dermis, both in interspaces and burn fields. This burn comb model with its newly developed fixed dorsal frame allows investigation of topical agents to treat BWP in partial-thickness burns.

Early monocyte modulation by the non-erythropoietic peptide ARA 290 decelerates AD-like pathology progression

Alzheimer's disease (AD) pathology is characterized by amyloid-β (Aβ) deposition and tau hyper-phosphorylation, accompanied by a progressive cognitive decline. Monocytes have been recently shown to play a major role in modulating Aβ pathology, and thereby have been pointed as potential therapeutic targets. However, the main challenge remains in identifying clinically relevant interventions that could modulate monocyte immune functions in absence of undesired off-target effects. Erythropoietin (EPO), a key regulator of erythrocyte production, has been shown to possess immunomodulatory potential and to provide beneficial effects in preclinical models of AD. However, the transition to use recombinant human EPO in clinical trials was hindered by unwanted erythropoietic effects that could lead to thrombosis. Here, we used a recently identified non-erythropoietic analogue of EPO, ARA 290, to evaluate its therapeutic potential in AD therapy. We first evaluated the effects of early systemic ARA 290 administration on AD-like pathology in an early-onset model, represented by young APP/PS1 mice. Our findings indicate that ARA 290 early treatment decelerated Aβ pathology progression in APP/PS1 mice while improving cognitive functions. ARA 290 potently increased the levels of total monocytes by specifically stimulating the generation of Ly6C^Low patrolling subset, which are implicated in clearing Aβ from the cerebral vasculature, and subsequently reducing overall Aβ burden in the brain. Moreover, ARA 290 increased the levels of monocyte progenitors in the bone marrow. Using chimeric APP/PS1 mice in which Ly6C^Low patrolling subset are selectively depleted, ARA 290 was inefficient in attenuating Aβ pathology and ameliorating cognitive functions in young animals. Interestingly, ARA 290 effects were compromised when delivered in a late-onset model, represented by aged APP1/PS1. In aged APP/PS1 mice in which AD-like pathology is at advanced stages, ARA 290 failed to reverse Aβ pathology and to increase the levels of circulating monocytes. Our study suggests that ARA 290 early systemic treatment could prevent AD-like progression via modulation of monocyte functions by specifically increasing the ratio of patrolling monocytes.

Second-generation non-hematopoietic erythropoietin-derived peptide for neuroprotection

Erythropoietin (EPO) is a well-known erythropoietic cytokine having a tissue-protective effect in various tissues against hypoxic stress, including the brain. Thus, its recombinants may function as neuroprotective compounds. However, despite considerable neuroprotective effects, the EPO-based therapeutic approach has side effects, including hyper-erythropoietic and tumorigenic effects. Therefore, some modified forms and derivatives of EPO have been proposed to minimize the side effects. In this study, we generated divergently modified new peptide analogs derived from helix C of EPO, with several amino acid replacements that interact with erythropoietin receptors (EPORs). This modification resulted in unique binding potency to EPOR. Unlike recombinant EPO, among the peptides, ML1-h3 exhibited a potent neuroprotective effect against oxidative stress without additional induction of cell-proliferation, owing to a differential activating mode of EPOR signaling. Furthermore, it inhibited neuronal death and brain injury under hypoxic stress in vitro and in an in vivo ischemic brain injury model. Therefore, the divergent modification of EPO-derivatives for affinity to EPOR could provide a basis for a more advanced and optimal neuroprotective strategy.

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Short peptides derived from helix C of EPO have a neuroprotective effect.

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Divergent modification of EPO-derived peptides has a differential affinity to EPOR.

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ML1 and its analogs have differential cell protective and proliferative effects.

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ML1-h3 protects neurons by suppressing in vitro oxidative stress.

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ML1-h3 mitigates brain injury in the in vivo mouse ischemic model without hematopoietic effect.

Senescence in a cell culture model for burn wounds

Thermal injuries cause severe damage on the cellular and tissue level and are considered especially challenging in the clinical routine. Complex interactions of different cell types and pathways dictate the formation of burn wounds. Thus, complications like burn wound progression, where so far viable tissue becomes necrotic and the size and depth of the wound increases, are difficult to explain, mainly due to the lack of simple model systems. We tested the behavior of human fibroblasts after heat treatment. A prominent response of the cells is to activate the heat shock response (HSR), which is one of the primary emergency mechanisms of the cell to proteotoxic stress factors such as heat. However, after a powerful but not lethal heat shock we observed a delayed activation of the HSR. Extending this model system, we further investigated these static cells and observed the emergence of senescent cells. In particular, the cells became β-galactosidase positive, increased p16 levels and developed a senescence-associated secretory phenotype (SASP). The secretion of cytokines like IL-6 is reminiscent of burn wounds and generates a bystander effect in so far non-senescent cells. In agreement with burn wounds, a wave of cytokine secretion enhanced by invading immune cells could explain complications like burn wound progression. A simple cell culture model can thus be applied for the analysis of highly complex conditions in human tissues.

Secondary Burn Progression Mitigated by an Adenosine 2A Receptor Agonist

BACKGROUND

Current burn therapy is largely supportive with limited therapies to curb secondary burn progression. Adenosine 2A receptor (A2AR) agonists have anti-inflammatory effects with decreased inflammatory cell infiltrate and release of pro-inflammatory mediators. Using a porcine comb burn model, we examined whether A2AR agonists could mitigate burn progression.

STUDY DESIGN

Eight full-thickness comb burns (4 prongs with 3 spaces per comb) per pig were generated with the following specifications: temperature 115° C, 3 kg force, and 30 second application time. In a randomized fashion, animals (4 per group) were then treated with A2AR agonist (ATL-1223, 3 ng/kg/min, intravenous infusion over 6 hours) or vehicle control. Necrotic interspace development was the primary outcome and additional histologic assessments were conducted.

RESULTS

Analysis of unburned interspaces (72 per group) revealed that ATL-1223 treatment decreased the rate of necrotic interspace development over the first 4 days following injury (p<0.05). Treatment significantly decreased dermal neutrophil infiltration at 48 hours following burn (14.63±4.30 vs 29.71±10.76 neutrophils/high-power field, p=0.029). Additionally, ATL-1223 treatment was associated with fewer interspaces with evidence of microvascular thrombi through post-burn day 4 (18.8% vs 56.3%, p=0.002). Two weeks following insult, the depth of injury at distinct burn sites (adjacent to interspaces) was significantly reduced by ATL-1223 treatment (2.91±0.47 vs 3.28±0.58 mm, p=0.038).

CONCLUSION

This work demonstrates the ability of an A2AR agonist to mitigate burn progression through dampening local inflammatory processes. Extended dosing strategies may yield additional benefit and improve cosmetic outcome in those with severe injury.

Erythropoietin enhances meniscal regeneration and prevents osteoarthritis formation in mice

Osteoarthritis (OA) is a leading cause of pain and disability, and knee is the most commonly afflicted joint. Meniscal tear due to injury or degeneration is an established factor for OA pathogenesis. Previous studies have demonstrated that meniscectomy does not reduce the OA incidence. We hypothesized that enhancing meniscal regeneration may prevent OA formation and progression. We first investigated the developmental pattern of mouse meniscus. Knee joint samples were collected at embryonic stages as well as after birth for histological and immunohistochemical studies. The results showed that meniscal cells underwent active proliferation and apoptosis at embryonic day 19.5 and Day 1 after birth. Collagen I (Col-1) is a major type of matrix protein in matured meniscus. Meniscal cells isolated from 3-month-old mice were used to examine the effect of selected factors on the molecules related to cell proliferation, angiogenesis, inflammation, extracellular matrix proteins and matrix degradation enzymes. Overall assessment indicated that EPO had optimal effect on meniscal regeneration. An organ culture system of mouse meniscus was established to test the effect of EPO on in vitro cultured menisci. EPO upregulated the expression of Col-1, Col-2 and VEGF-A, and downregulated the expression of MMP-13. Finally, we established a mouse model of meniscus injury induced OA (MIO), and mice were subjected to PBS or EPO treatments. The results demonstrated that EPO enhanced meniscal repair and prevented OA formation. EPO may become an effective Disease Modifying Osteoarthritis Drug and may be used for early treatment for meniscal injury to prevent OA progression.

The Dynamics of the Skin's Immune System

The skin is a complex organ that has devised numerous strategies, such as physical, chemical, and microbiological barriers, to protect the host from external insults. In addition, the skin contains an intricate network of immune cells resident to the tissue, crucial for host defense as well as tissue homeostasis. In the event of an insult, the skin-resident immune cells are crucial not only for prevention of infection but also for tissue reconstruction. Deregulation of immune responses often leads to impaired healing and poor tissue restoration and function. In this review, we will discuss the defensive components of the skin and focus on the function of skin-resident immune cells in homeostasis and their role in wound healing.

Activation of the β-common receptor by erythropoietin impairs acetylcholine-mediated vasodilation in mouse mesenteric arterioles

Clinically, erythropoietin (EPO) is known to increase systemic vascular resistance and arterial blood pressure. However, EPO stimulates the production of the potent vasodilator, nitric oxide (NO), in culture endothelial cells. The mechanism by which EPO causes vasoconstriction despite stimulating NO production may be dependent on its ability to activate two receptor complexes, the homodimeric EPO (EPOR2 ) and the heterodimeric EPOR/β-common receptor (βCR). The purpose of this study was to investigate the contribution of each receptor to the vasoactive properties of EPO. First-order, mesenteric arteries were isolated from 16-week-old male C57BL/6 mice, and arterial function was studied in pressure arteriographs. To determine the contribution of each receptor complex, EPO-stimulating peptide (ESP), which binds and activates the heterodimeric EPOR/βCR complex, and EPO, which activates both receptors, were added to the arteriograph chamber 20 min prior to evaluation of endothelium-dependent (acetylcholine, bradykinin, A23187) and endothelium-independent (sodium nitroprusside) vasodilator responses. Only ACh-induced vasodilation was impaired in arteries pretreated with EPO or ESP. EPO and ESP pretreatment abolished ACh-induced vasodilation by 100% and 60%, respectively. EPO and ESP did not affect endothelium-independent vasodilation by SNP. Additionally, a novel βCR inhibitory peptide (βIP), which was computationally developed, prevented the impairment of acetylcholine-induced vasodilation by EPO and ESP, further implicating the EPOR/βCR complex. Last, pretreatment with either EPO or ESP did not affect vasoconstriction by phenylephrine and KCl. Taken together, these findings suggest that acute activation of the heterodimeric EPOR/βCR in endothelial cells leads to a selective impairment of ACh-mediated vasodilator response in mouse mesenteric resistance arteries.

Burns: Pathophysiology of Systemic Complications and Current Management

As a result of many years of research, the intricate cellular mechanisms of burn injury are slowly becoming clear. Yet, knowledge of these cellular mechanisms and a multitude of resulting studies have often failed to translate into improved clinical treatment for burn injuries. Perhaps the most valuable information to date is the years of clinical experience and observations in the management and treatment of patients, which has contributed to a gradual improvement in reported outcomes of mortality. This review provides a discussion of the cellular mechanisms and pathways involved in burn injury, resultant systemic effects on organ systems, current management and treatment, and potential therapies that we may see implemented in the future.

ARA290, a Specific Agonist of Erythropoietin/CD131 Heteroreceptor, Improves Circulating Endothelial Progenitors' Angiogenic Potential and Homing Ability

BACKGROUND

Alternate erythropoietin (EPO)-mediated signaling via the EPOR/CD131 heteromeric receptor exerts the tissue-protective actions of EPO in a wide spectrum of injuries, especially ischemic diseases. Circulating endothelial progenitor cells contribute to endothelial repair and post-natal angiogenesis after chronic ischemic injury. This work aims to investigate the effects of ARA290, a specific agonist of EPOR/CD131 complex, on a subpopulation of endothelial progenitor cells named endothelial colony-forming cells (ECFCs) and to characterize its contribution to ECFCs-induced angiogenesis after peripheral ischemia.

METHODS

ARA290 effects on ECFCs properties were studied using cell cultures in vitro. We injected ARA290 to mice undergoing chronic hindlimb ischemia (CLI) in combination with ECFC transplantation. The homing of transplanted ECFC to ischemic tissue in vivo was assessed by SPECT/CT imaging.

RESULTS

In vitro, ARA290 enhanced the proliferation, migration, and resistance to H2O2-induced apoptosis of ECFCs. After ECFC transplantation to mice with CLI, a single ARA290 injection enhanced the ischemic/non-ischemic ratio of hindlimb blood flow and capillary density after 28 days and the homing of radiolabeled transplanted cells to the ischemic leg 4 h after transplantation. Prior neutralization of platelet-endothelial cell adhesion molecule-1 (CD31) expressed by the transplanted cells inhibited ARA290-induced improvement of homing.

DISCUSSION

ARA290 induces specific improvement of the biological activity of ECFCs. ARA290 administration in combination with ECFCs has a synergistic effect on post-ischemic angiogenesis in vivo. This potentiation appears to rely, at least in part, on a CD31-dependent increase in homing of the transplanted cells to the ischemic tissue.

Activation of the EPOR-β common receptor complex by cibinetide ameliorates impaired wound healing in mice with genetic diabetes

Diabetes is characterized by poor wound healing which currently lacks an efficacious treatment. The innate repair receptor (IRR) is a master regulator of tissue protection and repair which is expressed as a response injury or metabolic stress, including in diabetes. Activation of the IRR might provide benefit for diabetic wound healing. A specific IRR agonist cibinetide was administered in an incisional wound healing model performed mice with genetic diabetes (db⁺/db⁺) and compared to the normal wild-type. Animals were treated daily with cibinetide (30μg/kg/s.c.) or vehicle and euthanized 3, 7, and 14days after the injury to quantitate vascular endothelial growth factor (VEGF), malondialdehyde (MAL), phospho-Akt (pAkt), phospho e-NOS (p-eNOS), and nitrite/nitrate content within the wound. Additional evaluations included quantification of skin histological change, angiogenesis, scar strength, and time to complete wound closure. Throughout the wound healing process diabetic animals treated with vehicle exhibited increased wound MAL with reduced VEGF, pAkt, peNOS and nitrite/nitrate, all associated with poor re-epitheliziation, angiogenesis, and wound breaking strength. Cibenitide administration significantly improved these abnormalities. The results suggest that cibinetide-mediated IRR activation may represent an interesting strategy to treat diabetes-associated wound healing.

Effects of erythropoietin receptor activity on angiogenesis, tubular injury, and fibrosis in acute kidney injury: a "U-shaped" relationship

The erythropoietin receptor (EpoR) is widely expressed but its renoprotective action is unexplored. To examine the role of EpoR in vivo in the kidney, we induced acute kidney injury (AKI) by ischemia-reperfusion in mice with different EpoR bioactivities in the kidney. EpoR bioactivity was reduced by knockin of wild-type human EpoR, which is hypofunctional relative to murine EpoR, and a renal tubule-specific EpoR knockout. These mice had lower EPO/EpoR activity and lower autophagy flux in renal tubules. Upon AKI induction, they exhibited worse renal function and structural damage, more apoptosis at the acute stage (<7 days), and slower recovery with more tubulointerstitial fibrosis at the subacute stage (14 days). In contrast, mice with hyperactive EpoR signaling from knockin of a constitutively active human EpoR had higher autophagic flux, milder kidney damage, and better renal function at the acute stage but, surprisingly, worse tubulointerstitial fibrosis and renal function at the subacute stage. Either excess or deficient EpoR activity in the kidney was associated with abnormal peritubular capillaries and tubular hypoxia, creating a "U-shaped" relationship. The direct effects of EpoR on tubular cells were confirmed in vitro by a hydrogen peroxide model using primary cultured proximal tubule cells with different EpoR activities. In summary, normal erythropoietin (EPO)/EpoR signaling in renal tubules provides defense against renal tubular injury maintains the autophagy-apoptosis balance and peritubular capillary integrity. High and low EPO/EpoR bioactivities both lead to vascular defect, and high EpoR activity overides the tubular protective effects in AKI recovery.

Neutrophil extracellular traps coincide with a pro-coagulant status of microcirculatory endothelium in burn wounds

Burn-induced tissue loss is partly related to secondary expansion of necrosis into vital dermis neighboring the initial burn injury. An important factor herein is the severe loss of perfusion of the burn wound, probably caused by microvascular damage induced by the intense local inflammatory responses as well as burn-induced hypercoagulation. We hypothesize that the formation of neutrophilic extracellular traps (NETs) play an important role in this. The purpose of this study was to investigate postburn intravascular thrombosis, NETs formation and the coagulant state in the microvasculature of burns in both animal models and patients. We used two in vivo burn wound models: rats and pigs. In rats, the entire wound was excised at day 14 postburn and in pigs burn wound biopsies were collected at different time points up to 60 days postburn. To confirm the data in patients, eschar from the burn wound was obtained from burn wound patients at different time points after wounding. The number of intravascular thrombi, the presence of intravascular NETs and the number of tissue factor (TF) positive blood vessels in the burn wound was determined. In rats, a significant increase in intravascular thrombi and TF expression was observed 14 days postburn, that in majority coincided with NETs. In pigs, a significant increase in intravascular thrombi and TF expression was found over time up to 60 days postburn, that in majority coincided with NETs too. Also in eschar of burn wound patients, a significant increase in intravascular thrombi was noted, that in majority coincided with NETs, already 0.5 days postburn and remained elevated up to 46 days postburn. This study shows the presence of NETosis in microcirculatory thrombosis of burn wounds and a switch in the microcirculatory endothelium toward a procoagulant phenotype.

Increased bone formation in a rabbit long-bone defect model after single local and single systemic application of erythropoietin

Background and purpose - Delayed bone healing with non-union is a common problem. Further options to increase bone healing together with surgery are needed. We therefore evaluated a 1-dose single application of erythropoietin (EPO), applied either locally to the defect or systemically during surgery, in a critical-size rabbit long-bone defect. Material and methods - 19 New Zealand White rabbits received a 15-mm defect in the radius diaphysis. An absorbable gelatin sponge was soaked with saline (control group and systemic treatment group) or EPO (local treatment group) and implanted into the gap. The systemic treatment group received EPO subcutaneously. In vivo micro-CT analysis was performed 4, 8, and 12 weeks postoperatively. Vascularization was evaluated histologically. Results - Semiquantitative histomorphometric and radiological evaluation showed increased bone formation (2.3- to 2.5-fold) in both treatment groups after 12 weeks compared to the controls. Quantitative determination of bone volume and tissue volume showed superior bone healing after EPO treatment at all follow-up time points, with the highest values after 12 weeks in locally treated animals (3.0- to 3.4-fold). More vascularization was found in both EPO treatment groups. Interpretation - Initial single dosing with EPO was sufficient to increase bone healing substantially after 12 weeks of follow-up. Local application inside the defect was most effective, and it can be administered directly during surgery. Apart from effects on ossification, systemic and local EPO treatment leads to increased callus vascularization.

3,4-Methylenedioxy-β-Nitrostyrene Ameliorates Experimental Burn Wound Progression by Inhibiting the NLRP3 Inflammasome Activation

BACKGROUND

Burn wound progression remains a challenging problem in the clinic. Secondary tissue damage caused by unlimited inflammatory response is considered to be one of the key factors contributing to this clinical problem. Nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome has recently been found to play important roles in immune activation and the inflammatory response after burn/trauma. This experimental study aims (1) to observe the expression and distribution of NLRP3 inflammasome in burn wounds of a rat burn model and (2) to study whether inhibiting the NLRP3 inflammasome activation would ameliorate burn wound progression.

METHODS

A deep second-degree burn was inflicted on the backs of Wistar rats. The expression of NLRP3 inflammasome components and interleukin-1β were determined by Western blot and coimmunoprecipitation. The distribution of NLRP3 inflammasome was assessed by immunohistochemical staining and double-labeling immunofluorescence. Neutrophil infiltration, wound perfusion, burn depth, and wound healing time were assessed.

RESULTS

Burn induced remarkable NLRP3 inflammasome activation and cleavage of interleukin-1β. The NLRP3 inflammasome was observed mainly in macrophages of the zone of stasis. 3,4-Methylenedioxy-β-nitrostyrene significantly inhibited NLRP3 inflammasome activation and inflammatory cytokine production in burn wounds. Consequently, neutrophil infiltration was reduced, wound perfusion was restored, burn wound progression was ameliorated, and wound healing was accelerated.

CONCLUSIONS

In this study, the authors demonstrated that burn induced NLRP3 inflammasome activation and inflammatory response in wounds, which may be associated with burn wound progression. Treatment with 3,4-methylenedioxy-β-nitrostyrene inhibited NLRP3 inflammasome activation, ameliorated burn wound progression, and promoted wound healing.

A Nonhematopoietic Erythropoietin Analogue, ARA 290, Inhibits Macrophage Activation and Prevents Damage to Transplanted Islets

BACKGROUND

Erythropoietin exerts anti-inflammatory, antiapoptotic, and cytoprotective effects in addition to its hematopoietic action. A nonhematopoietic erythropoietin analogue, ARA 290, has similar properties. The efficacy of pancreatic islet transplantation (PITx) is reduced due to islet damage that occurs during isolation and from the severe inflammatory reactions caused by the transplantation procedure. We investigated whether ARA 290 protects islets and ameliorates inflammatory responses following PITx thus improving engraftment.

METHODS

The effects of ARA 290 on pancreatic islets of C57BL/6J (H-2) mice and on murine macrophages were investigated using an in vitro culture model. As a marginal PITx, 185 islets were transplanted into the liver of streptozotocin-induced diabetic mice (H-2) via the portal vein. Recipients were given ARA 290 (120 μg/kg) intraperitoneally just before and at 0, 6, and 24 hours after PITx. Liver samples were obtained at 12 hours after PITx, and expression levels of proinflammatory cytokines were assessed.

RESULTS

ARA 290 protected islets from cytokine-induced damage and apoptosis. Secretion of pro-inflammatory cytokines (IL-6, IL-12, and TNF-α) from macrophages was significantly inhibited by ARA 290. After the marginal PITx, ARA 290 treatment significantly improved the blood glucose levels when compared to those of control animals (P < 0.001). Upregulation of monocyte chemoattractant protein-1, macrophage inflammatory protein-1β, IL-1β, and IL-6 messenger RNA expression within the liver was suppressed by ARA 290 treatment.

CONCLUSIONS

ARA 290 protected pancreatic islets from cytokine-induced damage and apoptosis and ameliorated the inflammatory response after PITx. ARA 290 appears to be a promising candidate for improvement of PITx.

Mesoporous Silica Particles as a Multifunctional Delivery System for Pain Relief in Experimental Neuropathy

The long-term use of potent analgesics is often needed to treat chronic pain. However, it has been greatly hindered by their side effects such as addiction and withdrawal reactions. The study seeks to circumvent these drawbacks by taking advantage of a multifunctional delivery system based on nanoparticles to target on pathological neuroinflammation. A drug delivery system is designed and generated using mesoporous silica nanoparticles (MSNs) that are loaded with Δ9-THC (Δ9-tetrahydrocannabinol, a cannabinoid) and ARA290 (an erythropoietin-derived polypeptide), both of which possess analgesic and anti-inflammatory functions. The actions of such THC-MSN-ARA290 nanocomplexes depend on the enhanced permeability and retention of THC through nanosized carriers, and a redox-sensitive release of conjugated ARA290 peptide into the local inflammatory milieu. The biosafety and anti-inflammatory effects of the nanocomplexes are first evaluated in primary microglia in vitro, and further in a mouse model of chronic constriction injury. It is found that the nanocomplexes attenuate in vitro and in vivo inflammation, and achieve a sustained relief of neuropathic pain in injured animals induced by both thermal hyperalgesia and mechanical allodynia. Thus, a nanoparticle-based carrier system can be useful for the amelioration of chronic neuropathic pain through combinatorial drug delivery.

Current concepts on burn wound conversion-A review of recent advances in understanding the secondary progressions of burns

Burn wound conversion describes the process by which superficial partial thickness burns convert into deeper burns necessitating surgical intervention. Fully understanding and thus controlling this phenomenon continues to defy burn surgeons. However, potentially guiding burn wound progression so as to obviate the need for surgery while still bringing about healing with limited scarring is the major unmet challenge. Comprehending the pathophysiologic background contributing to deeper progression of these burns is an essential prerequisite to planning any intervention. In this study, a review of articles examining burn wound progression over the last five years was conducted to analyze trends in recent burn progression research, determine changes in understanding of the pathogenesis of burn conversion, and subsequently examine the direction for future research in developing therapies. The majority of recent research focuses on applying therapies from other disease processes to common underlying pathogenic mechanisms in burn conversion. While ischemia, inflammation, and free oxygen radicals continue to demonstrate a critical role in secondary necrosis, novel mechanisms such as autophagy have also been shown to contribute affect significantly burn progression significantly. Further research will have to determine whether multiple mechanisms should be targeted when developing clinical therapies.

The Role of CHI3L1 (Chitinase-3-Like-1) in the Pathogenesis of Infections in Burns in a Mouse Model

In severe burn injury the unique setting of a depleted, dysfunctional immune system along with a loss of barrier function commonly results in opportunistic infections that eventually proof fatal. Unfortunately, the dynamic sequence of bacterial contamination, colonization and eventually septic invasion with bacteria such as Pseudomonas species is still poorly understood although a limiting factor in clinical decision making. Increasing evidence supports the notion that inhibition of bacterial translocation into the wound site may be an effective alternative to prevent infection. In this context we investigated the role of the mammalian Chitinase-3-Like-1 (CHI3L1) non-enyzmatic protein predominately expressed on epithelial as well as innate immune cells as a potential bacterial-translocation-mediating factor. We show a strong trend that a modulation of chitinase expression is likely to be effective in reducing mortality rates in a mouse model of burn injury with superinfection with the opportunistic PA14 Pseudomonas strain, thus demonstrating possible clinical leverage.

Low Oxygen Tension Primes Aortic Endothelial Cells to the Reparative Effect of Tissue-Protective Cytokines

Erythropoietin (EPO) has both erythropoietic and tissue-protective properties. The EPO analogues carbamylated EPO (CEPO) and pyroglutamate helix B surface peptide (pHBSP) lack the erythropoietic activity of EPO but retain the tissue-protective properties that are mediated by a heterocomplex of EPO receptor (EPOR) and the β common receptor (βCR). We studied the action of EPO and its analogues in a model of wound healing where a bovine aortic endothelial cells (BAECs) monolayer was scratched and the scratch closure was assessed over 24 h under different oxygen concentrations. We related the effects of EPO and its analogues on repair to their effect on BAECs proliferation and migration (evaluated using a micro-Boyden chamber). EPO, CEPO and pHBSP enhanced scratch closure only at lower oxygen (5%), while their effect at atmospheric oxygen (21%) was not significant. The mRNA expression of EPOR was doubled in 5% compared with 21% oxygen, and this was associated with increased EPOR assessed by immunofluorescence and Western blot. By contrast, βCR mRNA levels were similar in 5% and 21% oxygen. EPO and its analogues increased both BAECs proliferation and migration, suggesting that both may be involved in the reparative process. The priming effect of low oxygen tension on the action of tissue-protective cytokines may be of relevance to vascular disease, including atherogenesis and restenosis.

ARA 290, a nonerythropoietic peptide engineered from erythropoietin, improves metabolic control and neuropathic symptoms in patients with type 2 diabetes

Although erythropoietin ameliorates experimental type 2 diabetes with neuropathy, serious side effects limit its potential clinical use. ARA 290, a nonhematopoietic peptide designed from the structure of erythropoietin, interacts selectively with the innate repair receptor that mediates tissue protection. ARA 290 has shown efficacy in preclinical and clinical studies of metabolic control and neuropathy. To evaluate the potential activity of ARA 290 in type 2 diabetes and painful neuropathy, subjects were enrolled in this phase 2 study. ARA 290 (4 mg) or placebo were self-administered subcutaneously daily for 28 d and the subjects followed for an additional month without further treatment. No potential safety issues were identified. Subjects receiving ARA 290 exhibited an improvement in hemoglobin A(1c) (Hb A(1c)) and lipid profiles throughout the 56 d observation period. Neuropathic symptoms as assessed by the PainDetect questionnaire improved significantly in the ARA 290 group. Mean corneal nerve fiber density (CNFD) was reduced significantly compared with normal controls and subjects with a mean CNFD >1 standard deviation from normal showed a significant increase in CNFD compared with no change in the placebo group. These observations suggest that ARA 290 may benefit both metabolic control and neuropathy in subjects with type 2 diabetes and deserves continued clinical evaluation.

A non-erythropoietic peptide derivative of erythropoietin decreases susceptibility to diet-induced insulin resistance in mice

BACKGROUND AND PURPOSE

The haematopoietic activity of erythropoietin (EPO) is mediated by the classic EPO receptor (EpoR) homodimer, whereas tissue-protective effects are mediated by a heterocomplex between EpoR and the β-common receptor (βcR). Here, we investigated the effects of a novel, selective ligand of this heterocomplex - pyroglutamate helix B surface peptide (pHBSP) - in mice fed a diet enriched in sugars and saturated fats.

EXPERIMENTAL APPROACH

Male C57BL/6J mice were fed a high-fat high-sucrose diet (HFHS) for 22 weeks. pHBSP (30 μg·kg(-1) s.c.) was administered for the last 11 weeks. Biochemical assays, histopathological and immunohistochemical examinations and Western blotting were performed on serum and target organs (liver, kidney and skeletal muscle).

KEY RESULTS

Mice fed with HFHS diet exhibited insulin resistance, hyperlipidaemia, hepatic lipid accumulation and kidney dysfunction. In gastrocnemius muscle, HFHS impaired the insulin signalling pathway and reduced membrane translocation of glucose transporter type 4 and glycogen content. Treatment with pHBSP ameliorated renal function, reduced hepatic lipid deposition, and normalized serum glucose and lipid profiles. These effects were associated with an improvement in insulin sensitivity and glucose uptake in skeletal muscle. Diet-induced overproduction of the myokines IL-6 and fibroblast growth factor-21 were attenuated by pHBSP and, most importantly, pHBSP markedly enhanced mitochondrial biogenesis in skeletal muscle.

CONCLUSIONS AND IMPLICATIONS

Chronic treatment of mice with an EPO derivative, devoid of haematopoietic effects, improved metabolic abnormalities induced by a high-fat high-sucrose diet, by affecting several levels of the insulin signalling and inflammatory cascades within skeletal muscle, while enhancing mitochondrial biogenesis.

Modulation of cellular stress response via the erythropoietin/CD131 heteroreceptor complex in mouse mesenchymal-derived cells

Tissue-protective properties of erythropoietin (EPO) have let to the discovery of an alternative EPO signaling via an EPO-R/CD131 receptor complex which can now be specifically targeted through pharmaceutically designed short sequence peptides such as ARA290. However, little is still known about specific functions of alternative EPO signaling in defined cell populations. In this study, we investigated effects of signaling through EPO-R/CD131 complex on cellular stress responses and pro-inflammatory activation in different mesenchymal-derived phenotypes. We show that anti-apoptotic, anti-inflammatory effects of ARA290 and EPO coincide with the externalization of CD131 receptor component as an immediate response to cellular stress. In addition, alternative EPO signaling strongly modulated transcriptional, translational, or metabolic responses after stressor removal. Specifically, we saw that ARA290 was able to overcome a TNFα-mediated inhibition of transcription factor activation related to cell stress responses, most notably of serum response factor (SRF), heat shock transcription factor protein 1 (HSF1), and activator protein 1 (AP1). We conclude that alternative EPO signaling acts as a modulator of pro-inflammatory signaling pathways and likely plays a role in restoring tissue homeostasis. Key message: Erythropoietin (EPO) triggers an alternative pathway via heteroreceptor EPO/CD131. ARA290 peptide specifically binds EPO/CD131 but not the canonical EPO/EPO receptor. Oxidative stress and inflammation promote cell surface expression of CD131. ARA290 prevents tumor necrosis factor-mediated inhibition of stress-related genes. Alternative EPO signaling modulates inflammation and promotes tissue homeostasis.

Effects of intraosseous erythropoietin during hemorrhagic shock in swine

Objective

To determine whether erythropoietin given during hemorrhagic shock (HS) ameliorates organ injury while improving resuscitation and survival.

Methods

Three series of 24 pigs each were studied. In an initial series, 50% of the blood volume (BV) was removed in 30 minutes and normal saline (threefold the blood removed) started at minute 90 infusing each third in 30, 60, and 150 minutes with shed blood reinfused at minute 330 (HS-50_BV). In a second series, the same HS-50_BV protocol was used but removing an additional 15% of BV from minute 30 to 60 (HS-65_BV). In a final series, blood was removed as in HS-65_BV and intraosseous vasopressin given from minute 30 (0.04 U/kg min⁻¹) until start of shed blood reinfusion at minute 150 (HS-65_BV+VP). Normal saline was reduced to half the blood removed and given from minute 90 to 120 in half of the animals. In each series, animals were randomized 1∶1 to receive erythropoietin (1,200 U/kg) or control solution intraosseously after removing 10% of the BV.

Results

In HS-50_BV, O₂ consumption remained near baseline yielding minimal lactate increases, 88% resuscitability, and 60% survival at 72 hours. In HS-65_BV, O₂ consumption was reduced and lactate increased yielding 25% resuscitability. In HS-65_BV+VP, vasopressin promoted hemodynamic stability yielding 92% resuscitability and 83% survival at 72 hours. Erythropoietin did not affect resuscitability or subsequent survival in any of the series but increased interleukin-10, attenuated lactate increases, and ameliorated organ injury based on lesser troponin I, AST, and ALT increases and lesser neurological deficits in the HS-65_BV+VP series.

Conclusions

Erythropoietin given during HS in swine failed to alter resuscitability and 72 hour survival regardless of HS severity and concomitant treatment with fluids and vasopressin but attenuated acute organ injury. The studies also showed the efficacy of vasopressin and restrictive fluid resuscitation for hemodynamic stabilization and survival.

Erythropoietin-derived nonerythropoietic peptide ameliorates experimental autoimmune neuritis by inflammation suppression and tissue protection

Experimental autoimmune neuritis (EAN) is an autoantigen-specific T-cell-mediated disease model for human demyelinating inflammatory disease of the peripheral nervous system. Erythropoietin (EPO) has been known to promote EAN recovery but its haematopoiesis stimulating effects may limit its clinic application. Here we investigated the effects and potential mechanisms of an EPO-derived nonerythropoietic peptide, ARA 290, in EAN. Exogenous ARA 290 intervention greatly improved EAN recovery, improved nerve regeneration and remyelination, and suppressed nerve inflammation. Furthermore, haematopoiesis was not induced by ARA 290 during EAN treatment. ARA 290 intervention suppressed lymphocyte proliferation and altered helper T cell differentiation by inducing increase of Foxp3+/CD4+ regulatory T cells and IL-4+/CD4+ Th2 cells and decrease of IFN-γ+/CD4+ Th1 cells in EAN. In addition, ARA 290 inhibited inflammatory macrophage activation and promoted its phagocytic activity. In vitro, ARA 290 was shown to promote Schwann cell proliferation and inhibit its inflammatory activation. In summary, our data demonstrated that ARA 290 could effectively suppress EAN by attenuating inflammation and exerting direct cell protection, indicating that ARA 290 could be a potent candidate for treatment of autoimmune neuropathies.

Erythropoietin, a novel repurposed drug: an innovative treatment for wound healing in patients with diabetes mellitus

Developing a new drug is expensive: the cost of going from bench to bedside is about $US1 billion. Therefore, the repurposing of an approved drug is potentially rewarding because it expands the drug's existing therapeutic profile and preempts additional development costs. As the safety profile of a repurposed drug is already well known, any new investigations could then focus on its efficacy and other therapeutic benefits. Recombinant erythropoietin (EPO) is a potential candidate for repurposing because the results of numerous studies have shown that systemic and topical EPO is therapeutically beneficial when it is administered to healthy and diabetic animals with acute and chronic skin wounds and burns. Moreover, the molecular mechanisms of EPO's actions have been elucidated: EPO acts on those nonhematopoietic cells which are involved in the innate immune response where it promotes cellular proliferation and differentiation, exerts its cytoprotective actions, and inhibits apoptosis. In this review, the mechanism of EPO's action in skin wound healing is reviewed, and its potential for treating acute and chronic skin wounds and stimulating tissue regeneration in diabetic patients is discussed.

Potential role of erythropoietin receptors and ligands in attenuating apoptosis and inflammation in critical limb ischemia

OBJECTIVE

Managing critical limb ischemia (CLI) is challenging. Furthermore, ischemic myopathy prevents good functional outcome after revascularization. Hence, we have focused on limiting the tissue damage rather than angiogenesis, which has traditionally been the motivation to develop nonsurgical treatments for CLI. Erythropoietin (EPO) protects ischemic tissue, and this property may also benefit CLI. The objective of this study was to examine the expression of the tissue-protective EPO receptor complex (EPOR-CD131 [β-chain of interleukin (IL)-3/IL-5/granulocyte macrophage colony-stimulating factor receptor]) in skeletal muscle obtained from humans with CLI. Because native EPO is thrombogenic, the antiapoptotic and anti-inflammatory effects of a nonhematopoietic helix-B peptide of EPO (ARA 290) were investigated on ischemic myotubes in vitro.

METHODS

Tissue was obtained from gastrocnemius muscle of 12 patients undergoing amputation for CLI and from 12 patients without limb ischemia. The expression of EPOR and CD131 was demonstrated by immunohistochemistry and Western blot. A validated in vitro model of myotube ischemia was used in which mature C2C12 myotubes were cultured 6 to 12 hours in a depleted media and gas mixture (20% CO2 and 80% N2). The myotubes were pretreated with EPO or ARA 290 before exposure to simulated ischemia. Apoptosis and cell death were determined by cleaved caspase-3 assay and lactate dehydrogenase release assay. Enzyme-linked immunosorbent assay measured the inflammatory cytokines.

RESULTS

EPOR and CD131 were expressed and significantly upregulated in CLI (average optical density [OD] in Western blot [control vs CLI] EPOR, 0.05 U vs 0.1 U; CD131, 0.10 U vs 0.22 U; P < .01). There was colocalization of EPOR and CD131 in the sarcolemma (cell membrane) of the skeletal myofiber. There was no difference in the distribution of colocalization between the CLI and the normal muscle. The ischemic myotubes treated by ARA 290 in vitro had a significantly decreased number of apoptotic cells (ischemia vs ischemia plus ARA 290: 71.1% vs 55.1%; P < .01), cleaved caspase-3 (OD of ischemia vs ischemia plus ARA 290: 0.15 U vs 0.02 U; P < .01), lactate dehydrogenase release (ischemia vs ischemia plus ARA 290: 32.5 U/L vs 21.3 U/L; P < .01), and IL-6 release (OD at 450 nm, ischemia vs ischemia plus ARA 290: 0.18 vs 0.13; P < .01).

CONCLUSIONS

This study demonstrates the expression and the upregulation of EPOR and CD131 in CLI and also shows that EPOR and CDI are colocalized in the cell membrane of both ischemic and control muscle fiber. The in vitro experiments demonstrate that ARA 290 decreases inflammation and apoptosis of ischemic myotubes. ARA 290 may potentially be used as adjunctive treatment for CLI.